NEWBURY ASTRONOMICAL SOCIETY
MONTHLY MAGAZINE - JUNE 2015
This will be the last magazine of this session – Next issue September 2015
NEW HORIZONS ARRIVES AT PLUTO 14th JULY
An artist’s impression of what
NASA’s ‘New Horizons’ Probe is now approaching Pluto
and will arrive at its closest approach to the Dwarf planet on
14th July. The probe was launched on 6 th January 2006 on
an Atlas V 551 rocket from Cape Canaveral, Florida bound
for Pluto and beyond. At its closest approach with Pluto it
will be just 10,000 kilometres from the surface of Pluto and
will take the first detailed images of the Dwarf Planet.
The image above is an artist’s impression of what New
Horizons might encounter on its very brief encounter with
Pluto. Some surface features have already been detected
during testing of the onboard cameras. Lighter patches on
the surface may be evidence of some kind of geological
eruptions but may also be the result of recent impacts on
the surface. There have also been hints of a possible thin
atmosphere around Pluto.
New Horizons might see on Pluto
Pluto is thought to be a giant snowball 2300 kilometres in
diameter comprised mainly of frozen Nitrogen, water ice and
a possible rocky core. Pluto’s largest satellite Charon is
1200 kilometres in diameter and also thought to be
comprised mainly of water ice.
In the 1840s, using Newtonian mechanics, Urbain Le Verrier,
a French mathematician, predicted the position of the thenundiscovered planet Neptune after analysing perturbations in
the orbit of Uranus. Subsequent observations of Neptune in
the late 19th century caused astronomers to speculate that
the orbit of Uranus was being disturbed by another planet
beyond the orbit of Neptune.
Pluto was discovered by a young researcher Clyde
Tombaugh on 18th February 1930, after nearly a year of
searching at the Lowell Observatory in Flagstaff, Arizona.
Tombaugh discovered a possible moving object on
photographic plates taken on 23 rd January and 29th January
of that year but a lesser-quality photograph taken on 21st
January helped confirm the movement. Pluto was originally
classified as the 9th planet in the Solar System but was redesignated as a Dwarf Planet after the discovery of many
similar objects beyond Neptune.
Watch out for the first images on the news and the NASA
‘New Horizons’ website around the 14th July.
NEXT NEWBURY ASTRONOMICAL SOCIETY MEETING
4th September
To be decided
Website:
www.newburyas.org.uk
NEXT NEWBURY BEGINNERS MEETING
16th September Starting in Astronomy and The Autumn Sky
Website:
www.naasbeginners.co.uk
The journey taken since launch on 6 th January 2006
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THE PERSEIDS, THE FIRST METEOR SHOWER OF THE 2015 – 2016 SEASON
Meteor showers are notoriously unpredictable. The exact
time of any spectacular increase in numbers or if the
meteors will be bright is almost impossible to predict as is
the clear weather needed to see them. However every year
on the evening of the 12th August there is a spectacular
display from the Perseid Meteor Shower.
Fortunately this year there will be no bright Moon on the 12th
August so even the fainter meteors should be visible. The
meteors of a shower appear to radiate from a point in the
sky that is called the ‘Radiant’. The meteors of this
particular shower appear to originate from a ‘Radiant’ point
in the constellation of Perseus. If the trail of any meteor that
is seen can be tracked back and found to have originated
from this radiant point it will be a Perseid. A few meteors
might appear to originate from other directions so these are
the meteors that might be seen randomly and not part of any
named shower. These are known as Sporadic Meteors.
One or two meteors every five to ten minutes may be
seen. Some might be quite faint and may be difficult to
see from a well-lit area in the towns. Some quite bright
meteors will be seen even from fairly light polluted
skies. These may appear any anywhere in the sky
from close to the radiant in the north to directly
overhead. With a clear sky it may be possible to follow
the tracks back through the constellations they passed
through to the radiant point in Perseus.
Richard Fleet from the Newbury Astronomical Society
captured many of the Perseid meteors last year on his
DSLR camera from his home in Pusey, Wiltshire. Here
are a couple of Richard’s pictures:
From a clear dark site, the constellation of Perseus can be
clearly seen as a line of stars stretching from the very
distinctive ‘W’ shape of Cassiopeia towards the northern
eastern horizon. See the chart below.
A Perseid meteor heading towards the Seven Sisters
The ‘Radiant’ of the Perseid Shower at 23:00
If the sky is clear the Milky Way (our galaxy) will be seen
rising up from the northern horizon passing through
Perseus, Cassiopeia and right across the sky though
Cygnus and the Summer Triangle. The bright star Capella
in the constellation Auriga will be twinkling noticeably close
to the northern horizon.
No special equipment is required to see meteors but it does
pay to make yourself comfortable for a meteor watch. It is
essential to dress to keep warm. A warm coat should be
worn along with a good thick pair of trousers or perhaps an
extra pair of trousers or long legged underwear can be worn
for additional comfort. It can get very cold during the night
even in the summer. A garden lounger will make the
observer much more comfortable and avoid getting a stiff
neck from looking up for too long. It will also allow an extra
blanket to be used if it is chilly.
Observing can start as soon as it is dark but there is likely to
be more meteors during the hour or two after midnight.
Position the lounger so that the northern horizon can be
seen. Look at about 45º above the horizon and anywhere
between west, through north and to the east. Meteors will
appear as a fast streak of light flashing across the sky.
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A composite of all Richard’s images
Other annual meteor showers are:
PERIOD
Jan 1 – Jan 4
April 10 – April 22
May 1 – May 8
June 17 – June 26
July 15 - Aug 15
July 15 - Aug 20
July 15 - Aug 25
July 27 – Aug 17
Oct 15 – Oct 25
Oct 26 - Nov 16
Nov 15 – Nov 19
Dec 9 – Dec 14
Dec 17 – Dec 24
SHOWER NAME
Quadrantids
Lyrids
Eta Aquarids
Ophiuchids
Delta Aquarids
Piscis Aquarids
Capricornids
Perseids
Orionids
Taurids
Leonids
Geminids
Ursids
MAXIMUM
Jan 3
April 2
May 4
June 19
July 27
July 31
Aug 2
Aug 12
Oct 21
Nov 3
Nov 18
Dec 13
Dec 23
WHAT MAKES OUR SEASONS
The daytime sky at midday on 21st June midsummer day (Summer Solstice)
In many of our articles and in astronomical presentations
we refer to the Ecliptic (the imaginary line along which
the Sun, Moon and planets appear to move across the
sky) but what exactly is the Ecliptic? Another question
we need to consider is: why does the Ecliptic appear
higher in the sky during the day in the summer and high
in the night sky during the winter. The chart above
shows the position of the Ecliptic on midsummer day this
year with the Sun appearing very high in the sky. The
diagram below shows the position of the Sun on the
Ecliptic on midwinter day, 22nd December this year.
The tilt of Earth’s axis is thought to have been caused
soon after the Sun and Planets were formed some 4.3
billion years ago. It is thought that another newly formed
planet, about the size of Mars, collided with Earth and
created our Moon. The impact completely destroyed the
other planet that we call Thea and almost destroyed
Earth. Fortunately for us the impact on Earth was off-set
from the centre and a large mass was knocked off the
edge to create the Moon. In the process Earth was
pushed over and the 23.4º tilt we see today was created.
The Sun on the Ecliptic on midwinter day
In the night sky the height of the Ecliptic is reversed so it
appears higher in the winter night sky and lower in the
winter daytime sky. This is of course due to the seasons
which are caused by the tilted axis of rotation of Earth.
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An artist’s impression of the Thea impact
The 23.4º tilt gives us our seasons and presents us with a
slightly more complex view of the solar system, the stars
and the rest of the universe around us.
We all know that the Earth makes a complete
revolution around the Sun (orbit) once every 365 days,
following an orbit that is elliptical in shape. This means
that the distance between the Earth and Sun which is
145 million kilometres (93 million miles) on average,
varies throughout the year. During the first week in
January Earth is about 2.5 million kilometres (1.6
million miles) closer to the sun. This is referred to as
the perihelion. The aphelion or the point, at which the
Earth is about 2.5 million kilometres farther away from
the Sun, occurs during the first week in July.
CELESTIAL POLE the axis of rotation projected from the
surface of Earth into the sky.
CELESTIAL EQUATOR the plane projected from the
surface of Earth at 90º between the Celestial Poles.
(Earth’s true equator tilted at 23.4º to the Solar System).
ECLIPTIC the plane of the orbits of the planets of the
Solar System (and our Moon). Superimposed on our sky
it is the imaginary line along which the Sun, Moon and
planets appear to move across the sky.
This may sound a bit at odds to what we know about
the seasons in the Northern Hemisphere but actually
the difference in distance is not significant in terms of
changing the climate and is not the reason why we
have seasons. Seasons are caused by the fact that
the Earth is tilted on its axis by 23.4°. The orientation
of the tilt with respect to space does not change during
the year and always points to a fixed point amongst the
fixed background of stars. The Northern Hemisphere is
tilted toward the Sun in June and away from the Sun in
December, as shown in the diagram below.
The position of the tilt produces the seasons
The winter solstice marks the shortest day and longest
night of the year. In the Northern Hemisphere, it
occurs when the Sun is directly over the Tropic of
Capricorn which is located at 23.4° south of the equator
and runs through Australia, Chile, southern Brazil, and
northern South Africa. At this time the northern axis
(North Pole) is tilted away from the Sun so at midday
the UK is at its most northerly position above the plane
of the Solar System ‘the Ecliptic’. The Sun therefore
appears to be at its lowest position in the sky.
The summer solstice marks the longest day and
shortest night of the year. The Sun is directly over the
Tropic of Cancer, located at 23.4° north of the equator
and runs through Egypt, United Arab Emirates, India,
and Mexico. At this time the northern axis (North Pole)
is tilted towards the Sun so at midday the UK is at its
most southerly position above the plane of the Solar
System ‘the Ecliptic’ and the Sun is at its highest
position in the sky. It is the tilt of Earth’s axis that
causes the Ecliptic (the plane of the Solar System) to
appear tilted at 23.4º across our sky.
This year, the Northern Hemisphere summer solstice
will occur at 16:38 GMT on 21st June. The winter
solstice will occur at 04:38 GMT on 22nd December.
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Diagram showing the tilt of Earth’s axis.
There are two reasons why it is warmer in the summer.
Firstly the heat from the Sun is concentrated over a
smaller area at the equator because the rays are hitting
the surface at a higher angle. During the winter, the UK is
located further north during the day so the rays are spread
over a larger area on the curved spherical surface. A
square metre illuminated by the Sun directly overhead (at
Earth’s equator) may be spread over two square metres
further to the north therefore each square metre will
receive only half the heat from the Sun. Secondly the light
from the Sun has to pass through more of the atmosphere
during the winter before reaching the surface.
The main effect of the seasons on astronomers is the
shorter nights in the summer. During the mid-summer
months the sky does not get truly dark in the UK because
the Sun is only just below the northern horizon even at
midnight. Although the ecliptic is high in the sky during
the day in summer, it is very low in the southern sky
during the summer nights. This reduces the seeing
(clarity of the view) when observing planets and the Moon
during the summer because we will be looking through
more of our atmosphere which is also more turbulent and
polluted closer to the horizon. Deep sky objects such as
nebulae and galaxies become more difficult to see due to
the reduced contrast of the lighter summer night sky.
THE SUMMER NIGHT SKY 2015
The chart above shows the night sky looking south at
about 23:00 on 15th June. The sky has been darkened
on the chart to allow interesting objects to be displayed
because the sky will not get fully dark. West is to the
right and east to the left. The curved line across the sky
is the ecliptic. This is the imaginary line along which the
Sun, Moon and planets appear to move across the sky.
The constellations through which the ecliptic passes are
known as the constellations of the ‘Zodiac’.
Constellations through which the ecliptic passes are
(west to east): Leo (the Lion), Virgo (the Virgin), Libra
(the Scales) Scorpius (the Scorpion), Orphiuchus (the
Serpent bearer) and Sagittarius (the Archer) is just
appearing over the south eastern horizon.
The most striking constellation now is the distinctive
shape of Leo (the Lion) looking rather like the crouching
Sphinx in Egypt. The brightest star in Leo is Regulus
located almost on the ecliptic. Because it is located very
close to the ecliptic it is often occulted by the Moon.
This occurs when the Moon passes in front of Regulus.
It is an interesting thing to observe and follow.
The most obvious feature of Leo is the distinctive back to
front question mark ‘?’ pattern of stars above Leo. This
is known as the ‘Sickle’ due to its resemblance to the
curved blade of a sickle tool used to cut hay and grass.
Although the constellation of Leo is quite large in the sky
it may be just a little difficult to find for the first time
especially in a light polluted sky. However once it is
found it is much easier to locate. The rest of Leo to the
east (left) of the ‘Sickle’ resembles the body and hind
quarters of a resting lion.
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To the east of Leo are the constellations of Coma
Berenices and Virgo. Coma Berenices has no bright
stars and no distinctive shape but on a clear night the
three brighter stars can be made out. Virgo has one
bright star called Spica that twinkles close to the horizon.
The whole area of sky around Leo, Coma Berenices and
Virgo hosts many galaxies. These are the galaxies of our
‘local cluster’ of nearby galaxies. Our own ‘Local Group’
of galaxies is grouped around two large spiral galaxies
one of which is our own Milky Way. The other is M31 the
Great Spiral Galaxy in Andromeda. Our local group of
‘close-by’ galaxies are part of this larger group of galaxies
which in turn is part of a super cluster of galaxies.
Further east is the rather faint constellation of Libra which
is well placed over the south eastern horizon. Libra is of
special interest this year because the beautiful ringed
planet Saturn is resting within its bounds.
To the east of Libra are the southern constellations of
Scorpius (the Scorpion) and Sagittarius (the Archer) the
upper regions of these two constellations are visible
above the southern horizon. North of Scorpius and
Sagittarius are the large constellation of Orphiuchus (the
Serpent) and the small constellation of Scutum. The sting
and tail of Scorpius can be found by looking for the
beautiful bright red star Antares. This is the 7th brightest
star in the sky and appears distinctly red to the naked
eye. It is a Red Super Giant with a diameter of about 880
times that of our Sun and is around 10,000 times brighter.
There are lots of Messier objects in this area with many
being a ‘must to look at’ with a telescope. M11 the Wild
Duck Cluster in Scutum is a lovely Open Cluster.
THE SOLAR SYSTEM THIS MONTH
MERCURY is very difficult to see very low in the east
before dawn. Not really observable.
VENUS is now just about as high as it gets above the
south western horizon in the evening sky. It is so bright
at magnitude -4.4 that it cannot be missed.
Chart showing Venus at sunset
As Venus moves further out from the Sun it is moving
closer to us and will appear larger. However as it
gradually gets larger it will become a thinner crescent
shape so its brightness will remain almost the same.
Venus will reach its greatest eastern elongation (and will
appear ‘half Moon’ shaped) on 6th June when it will be at
its greatest apparent distance from the Sun.
SATURN rises at about 17:45 mid-month and will be well
positioned for observing quite low in the south from about
midnight until the sky begins to brighten. Saturn can be
seen in the south and will be observable until about 02:30
when it sets in the west. Although the ring system is wide
open the views of Saturn will not be great because it is
located very low on the ecliptic in the south For those living
in the southern hemisphere the views will be breathtaking
with Saturn high on their winter ecliptic. It is also possible
to see Saturn’s largest moon Titan using a small telescope
and up to six moons using a larger telescope.
The position of Titan during June 2015
URANUS rises in the east at about 01:00 so will be just
observable in the early morning before sunrise.
NEPTUNE rises in the east at about 23:55 so will be well
placed for observing in the early hours this month.
THE SUN
Venus at 21:00 1st June
Venus at 21:00 30th June
The images above show how Venus will be appearing
larger but narrower through the month of June.
The Sun rises at 03:45 at the beginning of the month and at
03:44 by the end of the month.
Sunspots and other activity on the Sun can be followed live
and day to day by visiting the SOHO website at:
http://sohowww.nascom.nasa.gov/ .
THE MOON PHASES IN JUNE 2015
MARS will not be visible this month as it will be lost in
the twilight glare as the Sun sets. See the Venus chart
above.
JUPITER is located in Cancer and will be in the south
west as the sky darkens. It will be visible until it sets in
the west at 23:00. See the Venus chart above. The
cloud belts and zones can be seen using a small
telescope. See the advice for observing Jupiter using a
telescope in the March issue of this magazine.
Jupiter is really past its best for this year but still in a
reasonably good position for observing in the west as
soon as the Sun sets. We are still looking straight down
on the equator and therefore see the moons passing in
front and behind the planet. This means we see the
moons cast an eclipse shadow on to the planet.
June will be the last time to have a worthwhile look at
Jupiter before it moves into conjunction with the Sun.
We will then have to wait until early next year before it
returns to the morning sky in the east.
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Full Moon will be on 2nd June
Last Quarter will be on 9th June
New Moon will be on the 16th June
First Quarter will be on 24th June
THE NIGHT SKY NEXT MONTH - JULY
The chart above shows the night sky as it appears on 15th July at 10 o’clock in the evening British Summer Time (BST).
As the Earth orbits the Sun and we look out into space each night the stars will appear to have moved across the sky by a
small amount. Every month Earth moves one twelfth of its circuit around the Sun, this amounts to 30 degrees each month.
There are about 30 days in each month so each night the stars appear to move about 1 degree. The sky will therefore
appear the same as shown on the chart above at 11 o’clock BST at the beginning of the month and at 9 o’clock BST at the
end of the month. The stars also appear to move 15º (360º divided by 24) each hour from east to west, due to the Earth
rotating once every 24 hours.
The centre of the chart will be the position in the sky directly overhead, called the Zenith. First we need to find some
familiar objects so we can get our bearings. The Pole Star Polaris can be easily found by first finding the familiar shape of
the Great Bear ‘Ursa Major’ that is also sometimes called the Plough or even the Big Dipper by the Americans. Ursa
Major is visible throughout the year from Britain and is always quite easy to find. This month it is in the north west. Look
for the distinctive saucepan shape, four stars forming the bowl and three stars forming the handle. Follow an imaginary
line, up from the two stars in the bowl furthest from the handle. These will point the way to Polaris which will be to the
north of overhead at about 50º above the northern horizon. Polaris is the only moderately bright star in a fairly empty
patch of sky. When you have found Polaris turn completely around and you will be facing south. To use this chart,
position yourself looking south and hold the chart above your eyes.
Planets observable in the night sky: Venus and Saturn.
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